The invention relates to a system and method for treatment of soot-laden water in a continuous flow completely mixed waste water treatment reactor system.
Controlling biological waste water treatment processing in the chemical industry requires balancing many competing elements. The waste water of the chemical industry frequently contains high levels of organic carbon, ammonia and nitrates. Thus the treatment procedure may require the simultaneous removal of organic carbon, ammonia, nitrates and other priority pollutants by a combination of nitrification and denitrification. The processing to form acetylene generates two complex waste water streams comprising a soot-containing waste water stream and an other process waste water stream. The soot-containing stream comprises very fine dispersed carbon particles and organic compounds such as, for example, benzene, toluene, and other volatile organic compounds in the water.
Nitrification, the biological oxidation of ammonia to nitrates by autotrophic bacteria, is typically utilized to remove ammonia from waste water. This process thus generates additional nitrates as the ammonia is oxidized. These autotrophic bacteria generally use carbon dioxide as a carbon source during the nitrification reaction. The nitrification is a sensitive process and requires, for example, prescribed temperatures, a specific pH range, and an aerobic environment with a dissolved oxygen content of generally more than 2 mg O2/L. In addition, excessive amounts of inhibitory compounds such as salts, certain amines, and other compounds must be avoided. Another requirement is a long Solids Retention Time (SRT), which means a balance of moderate organic carbon levels in proportion to ammonia, to allow the slowly growing autotrophic bacteria to complete with the faster growing heterotrophic bacteria found in the waste water.
Denitrification, the biological reduction of nitrates to nitrogen gas with the utilization of the organic carbon waste by heterotrophic bacteria, is typically used to remove nitrates and organic carbons from the waste water. The primary requirements for denitrification include an anoxic environment with a dissolved oxygen content of less than 0.5 mg O2/L and adequate organic carbon substrate to balance the nitrate levels. Without adequate organic carbon, the heterotrophic bacteria can not reduce the nitrates. Thus, the dissolved oxygen requirements for nitrification and denitrification are mutually exclusive.
Several processes have been developed in an attempt to handle waste water having high levels of organic carbon, ammonia and nitrates using the nitrification and denitrification reactions. One process is a two sludge system that employs anoxic conditions with heterotrophic bacteria to consume organic carbon and reduce nitrates in a first bioreactor with solids recycling and a second independent bioreactor system under aerobic conditions to oxidize the ammonia. This process has the advantage of completely separating the nitrification and denitrification steps and is used where nitrates are present in the influent, but it is not able to denitrify the nitrates generated in the nitrification step. This inability can be a significant problem when the level of ammonia in the influent is high.
Another process employs a single sludge system with two or more bioreactors. In this process, anoxic conditions are maintained in one vessel to facilitate denitrification while aerobic conditions are maintained in another vessel (or vessels) to facilitate nitrification. This arrangement is suitable to consume nitrates present in the influent waste water, but also suffers from an inability to denitrify the generated nitrates from the oxidation of ammonia. One way to manage nitrification and denitrification in a single sludge process involves an internal recirculation step. This internal recirculation step is employed in the “Carousel” process, oxidation ditches and the Modified Ludzak-Ettinger (MLE) process. These processes function by creating different process conditions spatially within a single plug flow reactor, and recirculating generated nitrates from the aerobic zone to the anoxic zone. These modified methods are suitable for plug flow reactors treating waste water in which toxic overloads of chemicals are not an issue.
Treating the soot-laden waste stream produced by formation of acetylene in either of these conventional systems is very difficult. The large amount of inert solids present in the soot waste water will quickly reduce the capacity of these activated sludge systems. Physical separation of the carbon solids generates a hazardous waste issue due to the organic compounds adsorbed to the soot. Treatment of the waste water with activate carbon would be very expensive. Thus, there is a need to develop an efficient and cost effective system to treat soot-laden waste water, and preferably such a system could utilize a portion of existing waste water treatment systems.